Conventionally, paper post-processing devices are commonly known for post-processing of paper fed from an image forming device. These paper post-processing devices receive and properly align paper which has been fed into a retaining device from an upstream image forming device, performs post-processing such as stapling when each unit (one set) of paper has been compiled, and then discharges the set.
However, with a normal post-processing device, the pitch of paper fed from the image forming device can be aligned upon receipt of each sheet of paper, but a great deal of time is lost when stapling multiple sheets of paper when a unit of predetermined number of pages has been retained in the retaining device, so handling each sheet of paper successively fed from the image forming device is not possible, and therefore the image forming process of the image forming device is commonly interrupted temporarily in order to relieve this condition. However, this causes the image forming process to be temporarily interrupted, and as result the efficiency will be lower for the image forming process including post-processing.
In contrast, the paper post-processing device of another conventional technology temporarily stores the first few sheets of paper from a set of paper which has been fed from the image forming device on the circumferential surface of a separate detour drum which acts as a second retaining device, and during this time, stapling is performed on a paper bundle which is one set of paper retained in the retaining device. The plurality of sheets of paper stored and retained on the detour drum are combined with the next sheet of paper fed from the image forming device and supplied to the empty retaining device where stapling of the previous paper bundle has been completed. By using this measure, the need to interrupt temporarily the image forming process is eliminated, and the processing efficiency for the image forming device can be increased.
However, if a paper of different size is included in the set of papers to form a so-called mixed bundle, a paper support member attached to a vertically angled retaining device which receives the bottom edge of the paper, must be raised or lowered depending on the size of the paper. Time is required for raising and lowering, and therefore synchronizing with the paper fed at a predetermined pitch from the image forming device is difficult.
In view of the above, an object of the present invention is to provide a paper alignment device which can perform post-processing of papers even with mixed sizes without a drop in processing efficiency, and to provide a paper post-processing device equipped with the same.